1. Technical Field
The present invention relates to polycyclic polymers and methods for their use in photolithographic applications. More specifically, the invention is related to the modification of polycyclic polymers containing pendant functional groups and to their uses in photoresist compositions for the manufacture of integrated circuits (IC""s).
2. Background
Trends in the electronics industry continually require IC""s that are faster, and consume less power. To meet these specifications the IC must be of a high density having sub-micron feature dimensions. Conducting lines must be made thinner and placed closer together. Reducing the spacing between conductive lines results in a concomitant increase in the efficiency of the IC enabling a greater storage capacity and faster processing of information on a computer chip. To achieve thinner line widths and smaller feature sizes higher patterning resolution is necessary.
The patterning of IC""s is carried out according to various lithography techniques known in the art. Photolithography employing ultraviolet (UV) light and increasingly deep UV light or other radiation is a fundamental and important technology utilized in the production of IC devices. A photosensitive polymer film (photoresist) is applied over a substrate surface (e.g., wafer) and dried. A photomask containing the desired patterning information is then placed in close proximity to the photoresist film. The photoresist is irradiated through the overlying photomask by one of several types of imaging radiation including UV light, electron beams, x-rays, or ion beams. Upon exposure to radiation, the photoresist undergoes a chemical change with attendant changes in solubility. After irradiation, the substrate is soaked in a solution that develops (i.e., selectively removes either the exposed or unexposed regions) the patterned selectively removes either the exposed or unexposed regions) the patterned images in the photosensitive polymer film. Depending on the type of photoresist used, or the polarity of the developing solvent, either the exposed or non exposed areas of film are removed in the developing process to expose the underlying substrate, after which the patterned exposed or unwanted substrate material is removed or changed by an etching process leaving the desired pattern in a functional layer of the wafer. The remaining photoresist material functions as a protective barrier against the etching process. Removal of the remaining photoresist material gives the patterned circuit. Etching is accomplished by plasma etching, sputter etching, and reactive ion etching (RIE).
Etching generally involves passing a gas through a chamber and ionizing the gas by applying a potential across two electrodes in the presence of the gas. The plasma containing the ionic species generated by the potential is used to etch a substrate placed in the chamber. The ionic species generated in the plasma are directed to the patterned substrate where they interact with the surface material forming volatile products that are removed from the surface. Reactive ion etching provides well defined vertical sidewall profiles in the substrate as well as substrate to substrate etching uniformity. Because of these advantages, the reactive ion etching technique has become the standard in IC manufacture.
In the manufacture of high density IC""s the coating, exposure, and development of the photoresist film is critical. It is important to control the line width of the imaged and developed photoresist to close tolerances. The profiles of the patterned photoresist structures must be straight with vertical sidewalls. In addition, the patterned resist must be tolerant to subsequent IC processing steps such as RIE. These high performance polymer resists require superior tuning of several polymer properties such as hydrophilicity, adhesion, differential solubilities between the radiation exposed and unexposed regions (e.g., good resolution and contrast capabilities) and RIE resistance. Accordingly, chemically amplified resist compositions are becoming favored in the manufacture of these high density IC devices.
U.S. Pat. No. 4,491,628 to Ito et al. discloses a chemically amplified photoresist composition containing a photosensitive acid generator and a polymeric component having pendant acid labile groups including t-butyl esters of carboxylic acids and t-butyl carbonates of phenols.
U.S. Pat. No. 5,372,912 to Allen et al. discloses a chemically amplified photoresist composition comprising an acrylate based copolymer, a phenolic binder and a photosensitive acid generator. The copolymer component comprises the reaction product of acrylic or methacrylic acid, alkyl acrylates or methacrylates, and a monomer having a pendant acid labile group such as t-butyl esters of carboxylic and t-butyl carbonates of phenols. The properties of the copolymer can be tailored by varying the content of the disclosed monomers.
International Patent Application Publication WO 97/33198 to The B.F. Goodrich Company discloses a chemically amplified photoresist composition comprising a polycyclic polymer containing repeating units having pendant acid labile groups. Additionally, the polymer may contain polycyclic repeating units having a variety of pendant neutral groups, acid groups, alkyl groups, and mixtures thereof. These polycyclic polymers have exhibited good transparency to short wave length imaging radiation while being resistant to RIE processing techniques. In addition, the wide variety of applicable functional groups enable the artisan to tailor the properties of the polymer to a wide range of specifications. The acid labile groups on the polymer are cleaved to confer polarity or solubility to the polymer, while the neutral groups function to impart hydrophilicity, solubility, promote wetting, and improve film properties. The pendant acid group contributes to the hydrophilicity/wetting of the polymer as well as conferring adhesive characteristics thereto. Pendant alkyl substituents are useful to vary the Tg of the polymer system.
While the foregoing polycyclic polymers exhibit flexibility in property tailoring for high performance photoresist applications through the use of selected pendant functional groups a drawback exists in that cycloolefinic monomers containing certain of these functionalities are difficult to efficiently polymerize directly. For example, hydroxyl (e.g., alcohols, carboxylic acids, phenols) and nitrogen (e.g., amides, nitriles) containing functionalities may inhibit the catalyst system utilized to polymerize these functional cycloolefin monomers, resulting in reduced yields of the desired polymer. In addition, cycloolefin monomers with certain functional groups may be difficult to synthesize and purify via conventional synthesis routes or might not always be commercially available. Accordingly there is a need for alternate synthesis routes for photoresist polymers having pendant functional groups that are technically feasible, efficient, and economical.
It is a general object of the invention to provide alternate methods for functionalizing polymers useful in photoresist compositions.
It is a further object of the invention to post-functionalize polymers comprising polycyclic repeating units.
It is still a further object of the invention to post-functionalize a polycyclic polymer comprising repeating units containing pendant acid labile moieties.
It is another object of the invention to provide alternate methods of functionalizing polycyclic polymers with hydroxyl, nitrogen and sulfur containing groups.
It is still another object of the invention to introduce carboxylic acid containing moieties into a polycyclic polymer backbone through a post-functionalization reaction.
It is another object of the invention to provide photoresist polymers with increased hydrophilicity.
It has been found that the above described objects of the present invention are accomplished by a method for preparing a polycyclic polymer suitable for use in photoresist compositions by introducing difficult to polymerize functionalities into the polymer via a post-functionalization process, said process comprising: (a) providing a polycyclic base polymer composition comprising repeating units containing pendant acid labile groups and repeating units containing pendant protected hydroxyl containing moieties; (b) deprotecting the hydroxyl containing moieties to give a free hydroxyl group; and (c) reacting the free hydroxyl group with a coreactive moiety to give a post-functionalized moiety.